Intra luminal spectroscopic analysis devices have been developed and commercialized. One application concerns the assessment of the state of blood vessel walls such as required in the diagnosis of atherosclerosis. This is an arterial disorder involving the intimae of medium- or large-sized arteries, including the aortic, carotid, coronary, and cerebral arteries. Atherosclerotic lesions or plaques can contain complex tissue matrices, including collagen, elastin, proteoglycans, and extracellular and intracellular lipids with foamy macrophages and smooth muscle cells. In addition, inflammatory cellular components (e.g., T lymphocytes, macrophages, and some basophiles) can also be found in these plaques.
The intra luminal spectroscopic analysis devices are used to extract information concerning the state of the vessels walls from the generated spectral information. Mathematical and statistical manipulations such as linear and non-linear regressions of the spectral band of interest and other multivariate analysis tools are available for building quantitative calibrations as well as qualitative models for discriminant analysis, enabling the detection and characterization of any vascular lesions.
One specific intra luminal spectroscopic analysis device uses an optical source, such as a tunable laser, to access or scan a spectral band of interest, such as a scan band in the near infrared of 750 nanometers (nm) to 2.5 micrometers (μm). The generated light is used to illuminate tissue in a target area in vivo using a catheter. Diffusely reflected light resulting from the illumination is then collected and transmitted to a detector system, where a spectral response is resolved.
This intra luminal spectroscopic device actually builds a “color picture” of the inner walls of the blood vessel. This is accomplished by rotating the head of the catheter while drawing the head through the region of interest of the vessel. This produces the spectral response within the scan band of the tunable laser for a series of points along a helical path across the vessels walls. These points are aligned into a raster image of the vessel wall for the region of interest.
Another potential problem associated with vessels is the formation of thrombus. A thrombus or blood clot is a product of coagulation within a blood vessel and typically appears as a semisolid mass, with the thrombus impeding or blocking the flow of blood through the vessel. Typically it includes platelets, red blood cells, white blood cells and/or fibrin. Thrombosis, i.e., the formation or presence of a clot or thrombus, can be caused by infection, trauma, injury, a slowing down or stagnation of blood flow past a point of injury, or rupture of an atherosclerotic plaque. In fact, disruption or rupture of atherosclerotic plaques appears to be the major cause of heart attacks and strokes, because, after the plaques rupture, local obstructive thromboses form within the blood vessels. Both venous and arterial thrombosis can occur. A coronary thrombus often initially forms at the site of rupture of a vulnerable plaque; i.e. at the location of a plaque with a lipid-rich core and a thin fibrous cap (thin-cap fibroatheroma or TCFA). Thus, locating a thrombus can help find the culprit lesion, a task that is difficult using the current practice of angiography when the lesion is non-stenotic. Approaches for managing thrombosis include treatment with anticoagulants and/or medication designed to dissolves the clot, bed rest or surgical removal.